I've tried some of the plastics in leech sizes, colors, never caught anything on 'em. Never used real live ones. I think they're icky and I don't wanna touch it. Kidding, but crawlers always seemed to work and leeches were harder to find. I'd be willing to give 'em a try next to crawlers just to see which would perform better. Might have to hit up Jimmy's.
I've used leeches on LSC and they work. I also have used them for perch on perch rigs, they also worked good. You can catch several perch on them before you have to rebait. They hold up much better than crawlers.